Fifty patients with either lymphoid or selected solid tumor malignancies were apheresed an identical number of times for PBSC collection after being randomized to receive either G-CSF 10 microg/kg/day alone (arm I), or G-CSF at the same dose with GM-CSF 5 microg/kg/day (arm II). Growth factor(s) was/were given as the stem cell mobilizing agent for 5 days before the start of PBSC collection, and were continued throughout the 4 days of apheresis. Aspiration and cryopreservation of autologous bone marrow occurred on day 3 or 4 of growth factor(s). Thirty-one of 50 patients received one cycle only at time of evaluation, and 19 patients received two cycles of HDCT, each supported with PBSC with or without autologous bone marrow. No patients received growth factors post-autologous stem cell transplant, unless the absolute neutrophils count (ANC) failed to recover to > or = 100/microl by day +18 post-transplant. The median number of days to recovery of ANC to 100/microl, 500/microl and 1000/microl, and of platelet counts to 20000/microl, 50000/microl and 100000/microl after either cycle 1 or cycle 2 of HDCT and the number of febrile days and platelet and PRBC transfusion requirements was not significantly different between the two arms of the study. The duration of hospitalization was similar between study arms for cycle 1 of HDCT, but was 3.5 days less with arm II compared to arm I (P = 0.0248) for cycle 2 of HDCT. The bone marrow buffy coat and PBSC product mononuclear cell count (x 10(8)/kg) and CD34+ cell count (x 10(6)/kg) collected by each method of stem cell mobilization was not significantly different. There is questionable clinical benefit with PBSC products mobilized with the combination of G-CSF and GM-CSF vs G-CSF alone. Perhaps different dosages, schedules, or other growth factor combinations with G-CSF might enhance these differences.